Propeller

ABSTRACT

A propeller has a stationary streamlined body of displacement which is provided with a leading end, a trailing end and an axis of symmetry passing through both of these ends. A propeller wheel is provided on the body of displacement, having a hub which is mounted at the leading end of the body and provided with an outer circumferential surface which merges tangentially with an outer circumferential surface of the body. The hub is rotatable about an axis of rotation coinciding with the axis of symmetry. Propeller blades are mounted on the hub for rotation with the same and project outwardly as well as axially beyond the hub in direction away from the leading end of the body of displacement. Each of the propeller blades has in the rotational direction of the hub a trailing edge, and also a curved leading edge which is longer than the trailing edge. The relationship of the maximum diameter of the body in a plane normal to the axis of symmetry relative to the maximum diameter of the propeller wheel in a plane normal to the axis of rotation is greater than 0.6:1.

United States Patent 1 1 Minnich 1 PROPELLER Willy Minnich, Windhukstrasse 9, 2 Hamburg 50, Germany 22 Filed: Aug; 15, 1973 211 Ap No. 388,625

[76] lnventor:

g 415/209 [51]" Int. Cl. F011) 25/28; F04D 3/00 [58] 'Field of Search 41.5/D1G; l, 129, 126, 209,

[56] References Cited 1 UNITED STATES PATENTS 1,851.513 3/1932 Holmstrom 415/D1G. 1 2,378,049 6/1945 Upson l t 415/121 G 2,763,426 9/1956 Erwin 415/159 2866594 12/1958 Quick 415/207 FOREIGN PATENTS OR APPLICATIONS 951,944 4/1949 France..... 415/159 1,142,112 3/1957 France 415/159 1,010,604 3/1952 France... 415/159 1,143,082 4/1957 France 415/126 344871 3/1931 United Kingdom. 415/D1G. 1

1052.221 9/1953 France 415/129 United Kingdom 415/201 1 51 Sept. 16-, 1975' Primary Examiner-Henryv Raduazo- V Attorney, Agent, or Firm.-Michael S.. S triker [57] ABSTRACT V A propeller has a stationary streamlined. body of displacement which is provided with a-leading end, a trailing end and an axis of Symmetry passing through both of these ends. A propeller wheel is providedon the body of displacement; having a hub which is mounted at the leading endof the body and provided with an outer circumferential surface which merges tangentially with an outer circumferential surface of the body. The hub is rotatable about'an axis of rotation coinciding with the axis of symmetry. Propeller blades are mounted on the hub for rotation with the same and project outwardly as well as axially beyond the hub in direction away from the. leading end of the body of displacement. Each of the propeller blades has in the rotational direction of the hub a trailing edge, and also a curved leading edge which is longer than the trailing edge. The relationship of then-maximum diameter of the body in a plane normal to the axis of symmetry relative to the maximum diameter of the propeller wheel in a plane normal to the axis of rotation is greater than 0.6: 1.

10 Claims, 7 Drawing Figures PAr mEn' m Y 3 905 719 SHEET 31. [1F 3 PATENTED 3.905.719

SHKET 2 [IF 3 PATENTEB-SEP'I 6 \975 sumau a 1 PROPELLER BACKGROUND )F Tl-lE iNvENTIoN flhe present invention relates to propellers, and in particularv to propellers which are highly suitable for .ship propulsion.

Conventional ship propellers are configurated as screw propellers, and many different types of such propellers have become known in the art. For purposes of the present invention it is not necessary to discuss the operationv of such propellers, which in any case is well known to those skilled in the art. However, it should be pointed out that it is a truism that the propulsive force of a screw propeller which is constructed to operate without cavitation cannot be increased by measures other than increasing the diameter of the propeller itself, short of destroyingtthe cavitation-free operating characteristic of the propeller.

The prior art has proposed to improve the effectiveness of screw propellers by associating with the propeller either guide baffles or coaxially arranged counterrotating-scrcws in order toovercome the undesirable twist formcdin the stream of liquid which is advanced by the propeller. lt is also known to locate a substantially pear-shaped body rearwardly or downstream of a screw propeller, in order to overcome the aforementioned twisting effect and the development of words rearwardly of the propeller. This body may be configurated as a rudder or as apart of a rudder, and may be provided with guide-baffles.

In 'the known screw propeller constructions those portions of the propeller blade which are located closely adjacent to the propeller hub contribute less to the development of propeller thrust than those portions which are further spaced from the hub. Based upon this realization there=exists another proposal in the prior art to so construct the propeller hub itself (or to combine it with a stationary body of displacement cooperating with the hub) that the water increments flowing "towards the propeller. are diverted ahead of the propeller blades outwardly of the region of the axis of rotation andare made to flow axially around the outer portions of the propeller blades. Another construction proposes to use a substantially'egg-shaped hull acting as a body of displacement and having propeller blades extending laterally out of it.

A characteristic which is common to all of these prior-art screw propellerconstructions is that .water is accelerated in generally axial direction once it enters between the blades of the propeller. -This;. however,

=- means that the pressure drop necessary for accelerating the water increments surrounding the propeller and flowing toward s the same, to be engaged by the blades thereof cannot befurther increased. lt follows from this that the throughput of water per unit of time through the propeller also cannot be increased, so that the effectiveness of the propeller, i.e., its thrust, cannot be improved in the prior-art constructions.

SUMMARY OF THE INVENTION is possible with a propeller of similar dimensions that is constructed according to the. prior art.

Another object of the invention is to provide such an improved propeller which affords the increased throughput of fluid by imparting to the fluid a radial component of acceleration in the propeller itself, and which thus provides for a substantial increase in thrust.

In keeping with these objects, and with others which will become apparent hereafter, one feature of the invention resides in a propeller, particularly a ships pro peller, which comprises a stationary streamlined body of displacement having a leading end, a trailing end and an axis of symmetry passing through said ends. A propeller wheel is provided, comprising a hub mounted on the body at the leading end thereof and having an outer circumferential surface which merges tangentially with an outer circumferential surface of the body. The hub is rotatable about an axis of rotation which coincides with the axis of symmetry. The propeller wheel further comprises a plurality of propeller blades mounted on the hub for rotation therewith and projecting outwardly u:- well as axially beyond the same in direction away from the leading end. Each of the propeller blades has in rotational direction of the hub a trailing edge and also a curved leading edge which is longer than the trailing edge. The relationship of the maximum diameter of the body in a plane normal to the axis of symmetry relative to the maximum'diameter of the propeller wheel in a plane normal to the axis of rotation is greater than 0.6:1. Advantageously. this relationship should be between 0.7 and 0.8:1. H

When the propeller wheel of the propeller according to the present invention is rotated, it causes in the fluid in which it rotates a main stream or flow which extends diagonally towards the circumference. This flow is to a significant extent developed due to centrifugal forces and is directed as a narrow stream along the rounded surface portions of the streamlined body at the leading end thereof, being diverted by these surface portions in axial direction towards the trailing end and being in the region of the converging trailing end retarded or decelerated while undergoing pressure conversion. The thusobtained low-loss deflection of the stream of fluid is based upon the effect of a pressure drop which develops in the region where the stream is deflected and re sults from the energy conversion which takes place in the stream..The pressure drop which takes place in the region where the strearn leaves the blades of the wheel results in a high meridian acceleration in the stream and causes a highmeridian speed at this point. This results in an improvement of the relationship'of the kinetic energy of the tangential component of movement with reference to the energy of the axial component of movement, leading to a partial recovery of the kinetic energy by conversion into pressure energy.

I have found, however, that it is important that a certain relationship of the maximum diameter of the body of displacement with respect to the diameter of the propeller wheel be maintained, in order to obtain the optimum flow conditions which are sought to be achieved with the present invention. If this relationship is satisfled, the essentially conical flow which is directed towards the circumference will develop sufficient centrifugal force to cause the desired substantial pressure differential in the propeller. In principle, this takes place without any energy losses. The substantial pressure drop in the region where fluid moves towards the propeller, particularly in the region adjacent the axis of rotation, results in a high throughput of fluid per unit of time. The pressure distribution at the hub ahd the body of displacement provides for a thrust component which acts upon the hub and the body of displacement and serves to relieve the propeller blades.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself. however. both as to its construction and its method of operation. together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic side view of the propeller according to the present invention;

FIG. 2 is a view of the propeller of FIG. I, looking towards the right in that Figure;

FIG. 3 is a diagrammatic axial section of the propeller in FIGS. 1 and 2, showing the fluid flow conditions when the propeller rotates and is in motion through the surrounding fluid;

FIG. 4 is a view similar to FIG. 3, but illustrating the fluid flow conditions when the propeller rotates but is otherwise stationary in the surrounding fluid;

FIG. 5 is a diagrammatic side view illustrating the propeller of FIGS. 1-4 mounted on the stern of a ship;

FIG. 6 is a partly sectioned'somewhat diagrammatic side view, illustrating a further embodiment of a propeller according to the present invention; and

FIG. 7 is a partly section diagrammatic side view illustrating an additional embodiment of the propeller according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing now in detail, and firstly referring to FIGS. 1 and 2, it will be seen that reference numeral 1 identifies a propeller shaft which is mounted for rotation in the usual manner, and which can be driven in rotation in the direction of the'arrow 7 by any suitable means well known to those skilled in the art. Mounted on the shaft 1 is a substantially conically configurat ed hub 2 which carries a plurality of propeller blades 3 (in the illustrated embodiment four of them) which together with the hub 2 constitute the propeller wheel. The spaces or channels between the adjacent blades 3 are to all intents and purposes open in all directions. There is further provided a body of displacement 4 which is streamlined, and which has a leading end (a left-hand one in FIG. 1) and a tapering or convergent trailing end (the right-hand one in FIG. 1). The body 4 does not rotate and is stationarily mounted, for instance by means of the mount II which connects it rigidly with the stern 12 of the fragmentarily shown ship that can be seen in FIG. 5. The hub 2 is located adjacent the leading end of the body of displacement 4, it being understood that a ship provided with the propeller according to the present invention will be propelled'towards the left in FIG. 1 when the propeller rotates in the direction of the arrow 7. The body 4is configurated so as to be rotationally symmetrical, thatis its outer circumferential surface is a surface of revolution. The body 4 has an axis of symmetry S which is coincident with the axis of rotation R of the shaft 1 and the ing end, that is into the outer circumferential surface of the body 4 at the leadingv end thereof.

As FIGS. I and 2 show clearly, the-body 4 is provided with generally axially directed small guide vanes 5 which are symmetrically distributed over its circumference. In the illustrated embodiment there are four. of these guide vanes 5 provided. although there could be more or fewer. Each of the blades 3 has a trailing edge 61: and a leading edge 6b, as seen with respect to the direction of rotation 7. In other words, the leading edge 6b is that at which fluid enters between the adjacent blades 3 and the trailing edge 6a is the one at which it is expelled from between the blades 3. The leading edges 6!: are curved and are substantially longer than the trailing edges 6a. It is particularly noticeable from FIG. 1 that the blades 3 extend not only outwardly from the hub 2, but also axially thereof in the direction away from the body 4 so as to define an unrestricted space which surrounds the shaft 1.

As FIG. 1 shows clearly. the blades 3 are inclined with respect to the axis of rotation R, and the angle of inclination can be chosen at will and in accordance with established principles of propeller construction. For instance, those portions of the blades which are closer to the hub 2 may be inclined to the axis R at obtuse angles which are greater than the angles at which the portions of the blades 3 that are more remote from the axis R are inclined to the latter. The blades may also be twisted in the direction of rotation, or opposite to the direction of rotation, or. be inclined or otherwise configurated. They may also be made so that they are adjustably mounted on the hub 2, to permit their angle of inclination with respect to the axis R to be changed at will, in order to make it possible to select an optimum angle of inclination in dependence upon the thrust which is required at any given time.

Referring now to FIG. 3, it will be seen that with the construction of FIGS. 1 and 2 it is possible to obtain a stream of fluid which is advanced by the novel propeller as the latter rotates and as the vehicle on which it is carried is.advanced in the fluid. This stream is designated in FIG. 3 with reference numerals 8 and 9. These flow lines 8 and 9 intersect the plane of F IG. 3, but for purposes of illustration they have been projected onto this plane. It will be seen that the outer or border lines 8 contact the outer tips 3a of the blades 3. They, in effect, constitute a tube of flowing water which surrounds the wheel 2, 3 and the body 4 at a small spacing 5. Within and without this tube the pressures are in equilibrium with the pressures of the water increments which move on the curved flow lines shown in FIG. 3. The cylindrical flow surface which constitutes the aforementioned tube acts. in effect, as an essentially friction-free tube wall containing that part of the stream which is inside of by the flow lines 9.'The tube surrounded by the flowing water which flows along the flow lines 8 is (in the direction from the left towards to the right in FIG. 3) of constantly decreasing cross section until the plane A-B is reached,'and its cross section thereupon constantly increases until the plane C-D is reached. Within this tube the mass of water propelled by the wheel 2, 3 flows towards the right in FIG. 3. Due tofthe construction of the wheel 2, 3 and in particular the fact thatit is, open in all directions, the wheel acts within this tube the manner of an axial propeller as 5 well as in the manner of a radial propeller, that is it combines the characteristics of both. v

In the spaces or channels defined between consecu tive ones of the blades 3 the water droplets or increments undergo meridian acceleration and reach their highest speed at'the narrowest cross-sectional region of the tube defined by the flow lines 8, that is at the region of the plane A -B. Once they pass beyond the plane A-B, they advance towards'the plane C-D. undergoing retardation or deceleration while at the same time the static pressure increases.

The mean meridian acceleration over the entire cross sectionsurroundedv by the tube defined by the flow lines 8, that is the mean acceleration which the water particles undergo during their movement in the direction towards the region of minimum pressure in the plane A-B, is dependent 'upon the relationship of the largest diameter of the body 4 (which is to be found in this plane A3) with reference to the largest diameter of the propeller wheel, that is the diameter in the plane E-F (see FIGS. 1 and 3). lt has been found that a relationship of the diameters in the planes A8 and BF greater and ().6:1 should be utilized in order to obtain the advantageous results of the present invention. Generally speaking, the relationship may vary between ().6:1 and 0.8:], and the currently preferred relationship is between 0.7:1 and 0.8:1 with approximately ().7:1 having been found to be the most advantageous relationship.

Where the flow lines 8, 9 diverge, the stream of propelled liquid has a component of movement which extends radially towards the axis of symmetry S of the body 4. Because of this, and because the product of the radial distance of a water increment from the axis S and its momentary circumferential speed is constant, the circumferential speed would increase and the energy conversion disadvantageously be influenced were it not for the fact that the small guide baffles 5, are provided on the body 4.

The stream which is expelled towards the right in FIG. 3 from the propeller wheel 2, 3 passes through the relatively narrow space 5, and becauseof this and also due to the fact that its kinetic energy issubstantially higher than the energy of the surrounding stream, the water flowing within the tube defined by the flow lines 8 can be deflected around and guidedby the rounded outer surface of the body 4 without any danger that the stream might lift off this surface even if the curvature of the surface is rather significant. This high kinetic energy of the stream facilitates the adherence of the stream to the body 4, even when the stream is retarded or decelerated. Moreover, in the region where the deceleration takes place the energy conversion is further facilitated by the fact that the homogeneity of the stream is improved due to the increase in kinetic energy which each increment of water undergoes during its movement towards the region of minimum pressure, that is the region of the plane A-B.

The energy conversion is completed in the region of the plane CD, that is shortly behind the body 4. In the plane C-D the cross section of the stream defined by the flow lines 8, 9 is equal to or greater than in the plane E-F, and it will thus be seen that the stream is not subject to a disadvantageous contraction of its cross section behind the propeller wheel 2, 3 or the entire propeller 2, 3, 4. The distribution of velocity of liquid particles in the stream in the cross section through b 6 whichthe plane C-D extends. is essentially uniform. The stream is highly resistant to deviations from optimum operating conditions.

FIG. 4 shows the behavior of the flow lines 8, 9 when the propeller of FIGS. 1 and 2 rotates but is otherwise stationary in the surrounding liquid, that is when, for instance, the ship on which it is mounted does not advance through the liquid. It will be seen that the water flows into the propeller wheel 2, 3 and leaves the same as an especially twist-free uniform stream.

Experiments have shown that the propeller according to the present invention develops a thrust which under the conditions of FIG. 4 is double that of conventional screw propellers, given identical propeller diameters and operation of the respective propellers in the cavitation-free range. Under the conditions shown in FIG. 3, where the propeller not only rotates but also advances with its associate ship through the liquid, the propeller according to the present invention develops 3 times the thrust of conventional screw propellers (when operated in accordance with considerations of maximum operating economy) and can propel the associated ship at twicethe speed afforded by conventional screw propellers.

If the direction of rotation of the novel propeller is reversed, the direction of thrust is also reversed, but the propeller will require more power input.

The propeller according to the present invention can be provided, as is shown in FIG. 6, with baffles or plates 14 which may be mounted in slots 13 extending inwardly from the outer circumferential surface of the body 4 and into which the plates 14 can be retracted or from which they can be extended to the position shown in FIG. 6 or even farther out. The manner in which the blades can be retracted and extended is entirely conventional, that is conventional devices can be provided for this purpose, for instance, screw spindles, linkage arrangements or the like. The plates 14 are distributed over the circumference of the body 4 so as to be located in or substantially in the plane A-B which is shown in FIG. 1. Their purpose is to afford a rapid braking action, because when they are extended to the position shown in FIG. 6 they deflect the stream of fluid radially away from the body 4, so that the thrust is immediately interrupted.

According to FIG. 7 the novel propeller according to t the present invention can also be used as a pivotable guide or rudder propeller. For this purpose it can be mounted on a shaft 16 which is to be secured to the hull of a ship and about which the body 4 can be pivoted in the direction of the double-headed arrow. The pivot axis defined by the shaft 16 extends transversely to the axis of symmetry S and the axis of rotation R (see FIG. 1) and the novel propeller can then be used as an auxiliary propeller for use in conjunction with a rudder. In fact, the propeller can be made a part of the rudder itself.

Because, in contradistinction to conventional auxiliary propellers used with rudders, the entire propeller drive can readily be accommodated in the body 4 itself, without any difficulties and without losing any effectiveness of the propeller, this solution is highly attractive and from a structural and operational point of view more advantageous than what is known from the prior art. In particular, the effectiveness of the novel propeller used in conjunction with the rudder is greater than what is known from the prior art.

The propeller according to the present invention-can also be provided with a baffle which circularly surrounds it to further influence the flow of the stream of liquid which is propelled by the wheel 2. 3. In addition to serving as an ideal ships propeller, the propeller according to the present invention may also be used in other applications, for instance, for the propulsion of gases, air or liquids in various types of fluid machines.

It will be understood that each of the elements described above. or two or more together, may alsofind a useful application in other types of contruetions differing from the type described above.

While the invention has been illustrated and described as embodied in a propeller, it is not intended to be limited to the details shown, since various modifications and other structural changes may be made with out departing in any. way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim: 1

l. A propeller for a water craft, comprising a stationary streamlined body of displacement having a leading end, a trailing end, and an axis of symmetry passing through said ends; and a propeller wheel, comprising a hub mounted adjacent said body at said leading end and having an outer circumferential surface which tangentially merges with an outer circumferential surface of said body, said hub being rotatable about an axis of rotation which coincides with said axis of symmetry, said propeller wheel further comprising a plurality of propeller blades mounted on said hub for rotation therewith, and projecting outwardly as well as a substantial distance forwardly beyond said hub in direction away from said leading end thus circumferentially surrounding an unrestricted space in the region where the dial plane including said axis of rotation, whereby said blades are so configuratcd that liquid is drawn from said unrestricted space in said region where said propeller blades extend forwardly beyond said hub and in between said leading edges, and the liquid is propelled toward said trailing edges and then along said stationary streamlined body in rearward direction substantially parallel to said axis of symmetry, the relationship of the maximum diameter of said body in a plane normal to said axis of symmetry relative to the maximum diameter of said propeller wheel in a plane normal to said axis of rotation being greater than 0.6:1.

2. A propeller as defined in claim 1, wherein the portions of said blades'which project forwardly beyond said hub surround said axis of rotation radially outwardly spaced therefrom.

3. A propeller as defined in claim 1, wherein said hub is of substantially conical configuration.

4. A propeller as defined in claim 1, wherein said outer circumferential surface of said body is configurated as a surface of revolution.

5. A propeller as defined in claim 1, wherein said blades each have an inner portion closer to and an outer portion farther spaced from said axis of rotation; and wherein said inner portions are inclined to said radial plane at smaller acuteangles than said outer portions.

6. A propeller as defined in claim I, wherein said blades are mounted on said hub so as to be adjustable relative to the same, for varying the angle included between the respective blade and said axis of rotation.

7. A propeller as defined in claim 1, and further comprising guide vanes provided on said outer circumferential surface of said body.

8. A propeller as defined in claim 1, further comprising mounting means for mounting said body and propeller wheel on a support for pivoting movement about a pivot axis extending transversely to the firstmentioncd axes.

9. A propeller as defined in claim 1, and further comprising fluid-flow diverting baffles provided on said body and extendable radially outwardly beyond said outer circumferential surface of the same.

10. A propeller as defined in claim 9, wherein said body is provided with slots extending inwardly from said outer circumferential surface, and wherein said baffles are received in respective ones of said slots and displaceable therein between a position in which the respective baffle is retracted into the associated slot and a position in which it extends outwardly beyond said outer circumferential surface of said body. 

1. A propeller for a water craft, comprising a stationary streamlined body of displacement having a leading end, a trailing end, and an axis of symmetry passing through said ends; and a propeller wheel, comprising a hub mounted adjacent said body at said leading end and having an outer circumferential surface which tangentially merges with an outer circumferential surface of said body, said hub being rotatable about an axis of rotation which coincides with said axis of symmetry, said propeller wheel further comprising a plurality of propeller blades mounted on said hub for rotation therewith, and projecting outwardly as well as a substantial distance forwardly beyond said hub in direction away from said leading end thus circumferentially surrounding an unrestricted space in the region where the propeller blades extend forwardly beyond said hub, said propeller blades each having a curved trailing edge and a leading edge which is curved to a substantially greater extent than said trailing edge and which leading edge is substantially longer than than said trailing edge, said propeller blades further having inner portions adjacent said hub and enclosing an acute angle with a radial plane including said axis of rotation, whereby said blades are so configurated that liquid is drawn from said unrestricted space in said region where said propeller blades extend forwardly beyond said hub and in between said leading edges, and the liquid is propelled toward said trailing edges and then along said stationary streamlined body in rearward direction substantially parallel to said axis of symmetry, the relationship of the maximum diameter of said body in a plane normal to said axis of symmetry relative to the maximum diameter of said propeller wheel in a plane normal to said axis of rotation being greater than 0.6:1.
 2. A propeller as defined in claim 1, wherein the portions of said blades which project forwardly beyond said hub surround said axis of rotation radially outwardly spaced therefrom.
 3. A propeller as defined in claim 1, wherein said hub is of substantially conical configuration.
 4. A propeller as defined in claim 1, wherein said outer circumferential surface of said body is configurated as a surface of revolution.
 5. A propeller as defined in claim 1, wherein said blades each have an inner portion closer to and an outer portion farther spaced from said axis of rotation; and wherein said inner portions are inclined to said radial plane at smaller acute angles than said outer portions.
 6. A propeller as defined in claim 1, wherein said blades are mounted on said hub so as to be adjustable relative to the same, for varying the angle included between the respective blade and said axis of rotation.
 7. A propeller as defined in claim 1, and further comprising guide vanes provided on said outer circumferential surface of said body.
 8. A propeller as defined in claim 1, further comprising mounting means for mounting said body and propeller wheel on a support for pivoting movement about a pivot axis extending transversely to the first-mentioned axes.
 9. A propeller as defined in claim 1, and further comprising fluid-flow diverting baffles provided on said body and extendable radially outwardly beyond said outer circumferential surface of the same.
 10. A propeller as defined in claim 9, wherein said body is provided with slots extending inwardly from said outer circumferential surface, and wherein said baffles are received in respective ones of said slots and displaceable therein between a position in which the respective baffle is retracteD into the associated slot and a position in which it extends outwardly beyond said outer circumferential surface of said body. 